Twenty-three-year-old Diana DeMayo was helping her millionaire boyfriend Peter Dabish move into his Detroit apartment last year when she was attacked, sustaining a series of blunt-force traumas to her head. After going on the run for weeks, Dabish eventually turned himself in to police and was charged with the first-degree murder of DeMayo in March.

DeMayo’s killing was one of 345 murders reported in the Detroit metropolitan area (Detroit-Livonia-Dearborn) last year. The high murder rate helped make the Motor City the most violent crime-prone area in the United States in 2010, with 1,111 violent crimes reported per 100,000 residents.

To compile our list of America’s most dangerous cities, we used the FBI’s uniform crime report for 2010, which tallies crime data for each of the country’s metropolitan statistical areas, regions that usually consist of a large city and its suburbs or clusters of closely linked smaller cities, and metropolitan divisions, which are core areas within some of the larger MSAs. Because small fluctuations in crime numbers can produce outsize jumps in rates in smaller metropolitan areas, we looked at MSAs with a population of 200,000 or more. We used the FBI's numbers for four categories of violent crimes: murder and non-negligent manslaughter; forcible rape; robbery; and aggravated assault.

It's commonly expected that crime will rise as economic conditions worsen, but that hasn't been the case in the U.S. – violent crime has fallen for the past four years. In 2010, murder was down 4%, rape fell 5%, robbery dropped 10%, and aggravated assault fell 4%, according to the FBI. “There’s a complex series of forces at work behind these rates,” says Tom Blomberg, dean of the College of Criminology and Criminal Justice at Florida State Univeristy. “The state of the economy, demographics, the number of young males at any given time, the rate of imprisonment and the number of police all factor in.”

In the case of Stockton, Calif., geography plays a large part in explaining the area's high rate of violence: 805 violent crimes per 100,000 residents, ranking seventh on our list. The city is a way station on a major drug route from Mexico up the West Coast, which leads to gang competition for turf, says Megan Wolfram, an intelligence analyst at the risk assessment firm iJET. "When you have competing gangs, there’s a rise in violence,” says Wolfram.

The nationwide drop in crime extends to several of our most dangerous cities, including the Memphis, Tenn., area, which comes in at No. 2 with 1,006 violent crimes per 100,000 residents, down from 1,146 the year before. “Many of [the bottom-most cities] are actually improving, it’s just that so are other cities at a higher rate,” says Wolfram, an intelligence analyst at iJET.